Let’s assume that:

Weight of bleaching powder = W gram

Used volume of hypo solution = V ml

Normality of hypo solution = N

The number of milli equivalents in SO-chlorine = the number of milli equivalents in iodine

= number of milli equivalents in Hypo

= N x V

Amount of chlorine = Milli equivalents x (1/1000) x Equivalent weight

= N x V x (1/1000) x 35.5

= 0.0355 x N x V

Percentage amount of chlorine available (by weight) = (0.0355 x N x V/W ) x 100